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  <title>Garbage collects unfinished XA transactions after severe errors</title>
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  <div id="layout-content"><div id="function.mysqlnd-ms-xa-gc" class="refentry">
 <div class="refnamediv">
  <h1 class="refname">mysqlnd_ms_xa_gc</h1>
  <p class="verinfo">(PECL mysqlnd_ms &lt; 1.6.0)</p><p class="refpurpose"><span class="refname">mysqlnd_ms_xa_gc</span> &mdash; <span class="dc-title">Garbage collects unfinished XA transactions after severe errors</span></p>

 </div>

 <div class="refsect1 description" id="refsect1-function.mysqlnd-ms-xa-gc-description">
  <h3 class="title">说明</h3>
  <div class="methodsynopsis dc-description">
   
   <span class="methodname"><strong>mysqlnd_ms_xa_gc</strong></span>
    ( <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$connection</code></span>
   [, <span class="methodparam"><span class="type">string</span> <code class="parameter">$gtrid</code></span>
   [, <span class="methodparam"><span class="type">bool</span> <code class="parameter">$ignore_max_retries</code></span>


  ]] ) : <span class="type">int</span></div>

  <p class="para rdfs-comment">
   Garbage collects unfinished XA transactions.
  </p>
  <p class="para">
    The XA protocol is a blocking protocol. There exist cases when servers
    participating in a global transaction cannot make progress when the transaction
    coordinator crashes or disconnects. In such a case, the MySQL servers
    keep waiting for instructions to finish the XA transaction in question.
    Because transactions occupy resources, transactions should always be
    terminated properly.
  </p>
  <p class="para">
    Garbage collection requires configuring a state store to track global
    transactions. Should a PHP client crash in the middle of a transaction
    and a new PHP client be started, then the built-in garbage collection
    can learn about the aborted global transaction and terminate it. If you
    do not configure a state store, the garbage collection cannot perform
    any cleanup tasks.
  </p>
  <p class="para">
    The state store should be crash-safe and be highly available to survive
    its own crash. Currently, only MySQL is supported as a state store.
  </p>
  <p class="para">
    Garbage collection can also be performed automatically in the background.
    See the plugin configuration directive <em>garbage_collection</em>
    for details.
  </p>
  <blockquote class="note"><p><strong class="note">Note</strong>: 
   <strong>Experimental</strong><br />
   <p class="para">
    The feature is currently under development. There may be issues and/or
    feature limitations. Do not use in production environments.
   </p>
  </p></blockquote>
 </div>


 <div class="refsect1 parameters" id="refsect1-function.mysqlnd-ms-xa-gc-parameters">
  <h3 class="title">参数</h3>
  <dl>

    
    <dt>
<code class="parameter">connection</code></dt>

    <dd>

     <p class="para">
      A MySQL connection handle obtained from any of the
      connect functions of the <a href="ref.mysqli.html" class="link">mysqli</a>,
      <a href="ref.mysql.html" class="link">mysql</a> or
      <a href="ref.pdo_mysql.html" class="link">PDO_MYSQL</a> extensions.
     </p>
    </dd>

   
   
    <dt>
<code class="parameter">gtrid</code></dt>

    <dd>

     <p class="para">
      Global transaction identifier (gtrid). If given, the garbage
      collection considers the transaction only. Otherwise,
      the state store is scanned for any unfinished transaction.
     </p>
    </dd>

   
    
    <dt>
<code class="parameter">ignore_max_retries</code></dt>

    <dd>

     <p class="para">
      Whether to ignore the plugin configuration <em>max_retries</em> setting.
      If garbage collection continuously fails and the <em>max_retries</em>
      limit is reached prior to finishing the failed global transaction,
      you can attempt further runs prior to investigating the cause
      and solving the issue manually by issuing appropriate SQL statements
      on the participants. Setting the parameter has the same effect
      as temporarily setting <em>max_retries = 0</em>.
     </p>
    </dd>

   

  </dl>

 </div>


 <div class="refsect1 returnvalues" id="refsect1-function.mysqlnd-ms-xa-gc-returnvalues">
  <h3 class="title">返回值</h3>
   <p class="para">
   Returns <strong><code>TRUE</code></strong> if garbage collection was successful. Otherwise, returns <strong><code>FALSE</code></strong>
  </p>
 </div>


 <div class="refsect1 seealso" id="refsect1-function.mysqlnd-ms-xa-gc-seealso">
  <h3 class="title">参见</h3>
  <p class="para">
   <ul class="simplelist">
    <li class="member">
     <a href="mysqlnd_ms.quickstart.xa_transactions.html" class="link">Quickstart XA/Distributed transactions</a>
    </li>
    <li class="member">
     <a href="mysqlnd_ms.configuration.html" class="link">Runtime configuration</a>
    </li>
    <li class="member">
      <a href="mysqlnd-ms.plugin-ini-json.html#ini.mysqlnd-ms-plugin-config-v2.xa" class="link">State store configuration</a>
    </li>
    <li class="member">
     <span class="function"><a href="mysqlnd_ms_get_stats.html" class="function" rel="rdfs-seeAlso">mysqlnd_ms_get_stats()</a> - Returns query distribution and connection statistics</span>
    </li>
   </ul>
  </p>
 </div>


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